-LRB- CNN -RRB- -- Rory McIlroy reclaimed golf 's No. 1 ranking without lifting a club after Ryder Cup teammate Luke Donald finished down the field in 37th at the RBC Heritage on Sunday .

Donald needed a top-eight finish to hold off the Northern Irishman but a four-over-par 75 in the opening round put him on the back foot straight away and he eventually finished 16 shots behind the winner , Carl Pettersson of Sweden .

McIlroy took the week off following a disappointing showing at the Masters , traveling to Copenhagen to support his tennis-playing girlfriend Caroline Wozniacki at her home tournament . The Dane 's bid for a third successive title in the event ended in defeat in Sunday 's final .

McIlroy is next scheduled to play at the PGA Tour 's Wells Fargo Championship at Quail Hollow , beginning May 3 -- a tournament he won in 2010 .

'' # 1 again without touching a golf club this week ... . I wish it was that easy ! '' the 22-year-old tweeted on Sunday .

Donald and McIlroy have swapped places three times this year already . The Englishman 's latest stint at the top lasted four weeks .

`` Is it a concern ? No , '' Donald said . `` Obviously , I 'd have liked to have played a bit more consistently this year . I built it up nicely last year through tournaments and winning a bunch . ''

Donald made the cut at the RBC Heritage with a second-round 69 but finished the tournament with two level-par rounds to end up on two over .

`` Not my best week , getting used to leaving this place ranked # 2 . Nice week off now , '' tweeted Donald , who lost out to Brandt Snedeker in a playoff at last year 's tournament .

Donald won the Transitions Championship in March but has only one other top-10 finish . McIlroy has four top-five finishes to go with his Honda Classic win in March .

Donald is next due to play at the Zurich Classic , beginning April 28 .

Pettersson , meanwhile , began the final round with a one-shot lead over Colt Knost and finished with a confident two-under 69 to move clear of the field for his fifth PGA Tour title .

Knost had a disastrous final round of 74 to drop out of contention , leaving Pettersson to claim victory by five strokes from another American , Zach Johnson .

Three years ago , the 34-year-old Pettersson dropped 30 pounds in a bid to slim down and improve his fitness , but found his swing was compromised and quickly decided to revert to his previous weight .

Describing how he put the pounds back on , Pettersson told the PGA Tour website : `` Well , you drink 10 beers and -LRB- eat -RRB- a tub of ice cream before bed . ''

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Luke Donald needed a top-eight finish at the RBC Heritage to keep No. 1 ranking

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Donald and Rory McIlroy have switched places three times already this season

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Sweden 's Carl Pettersson won the tournament by five shots from Zach Johnson